1. Field of the Invention
The present invention relates to low viscosity aromatic polyester polyols having an average functionality of about two and methods for preparing such polyols. In particular, the invention relates to low viscosity aromatic polyester polyols having an average functionality of about two formed by inter-esterification of a phthalic acid based material with diethylene glycol, a higher functional polyol having an average functionality of greater than two, and a long chain alkyl acid, ester or oil. The resulting aromatic polyester polyol has an average functionality of about two and has a lower dynamic viscosity as compared to the esterification product of a phthalic acid based material with diethylene glycol alone.
2. Description of the Related Art
Polyols are useful reactants in preparing a variety of polymeric or resin compositions. Aromatic polyester polyols are widely used in the manufacture of polyurethane and polyurethane-polyisocyanurate foams and resins. Typically, polyols are employed in reactions involving curing or crosslinking with polyisocyanate materials having at least two isocyanate groups per mole, reactions involving melamines or formaldehyde resins, and esterification reactions with unsaturated monobasic fatty acids to form alkyl resins.
Aromatic polyester polyols are attractive because they tend to be low in cost, yet can be used to produce a wide variety of cellular foams having excellent properties and adaptable for many end use applications. One class of aromatic polyester polyols that has enjoyed wide commercial success comprises the polyol products produced by esterification of phthalic acid or phthalic acid anhydride with an aliphatic polyhydric alcohol. For example, a diethylene glycol phthalate is available commercially from Stepan Company, Northfield, Ill. Such a polyol is a somewhat viscous liquid product, with a desirably high aromatic ring content, and a desirably low acid number. This type of polyester polyol is capable of reacting with organic isocyanates to produce, for example, coatings, adhesives, sealants, and elastomers (xe2x80x9cCASE materialsxe2x80x9d), that can have excellent characteristics, such as tensile strength, adhesion, and abrasion resistance.
One problem generally encountered when using aromatic polyester polyols is that they are characteristically high in dynamic viscosity, making handling very difficult. Often, aromatic polyester polyols must be diluted or dissolved in relatively large amounts of a suitable solvent to enable producing low viscosity, easy-to-apply coating compositions upon being mixed with a curing or crosslinking agent.
Ideally, an aromatic polyester polyol has a dynamic viscosity that is sufficiently low to allow ease of pumping and mixing without the use of solvents or other viscosity modifying additives. An aromatic polyester polyol having too great a dynamic viscosity can cause difficulties in transfer of the material, as for example from storage to reactor or from the final product to the final application of the product. Excessive dynamic viscosity also can be a serious obstacle to efficient mixing with other CASE material ingredients, such as an isocyanate. Several solutions to this viscosity problem have been offered. See, for example, U.S. Pat. No. 4,644,027 (to Stepan Company) and U.S. Pat. No. 4,812,533 (to CasChem, Inc.), and Romanian Pat. App. 83,203. See also, for example, Liu, D. et al., Tuliao Gengye, 1988, 5, 1-3: High Solid alkylated Resin Baked Paint (Shenyang Inst. Chem. Co.). However, these prior art solutions are often complicated, expensive, difficult to readily implement, and may produce a polyol having a functionality of less than 2.
Thus, there is a need for low viscosity aromatic polyester polyols having an average functionality of about two that are economical to produce and can be converted into cellular foams and other CASE materials having excellent properties.
The present invention relates to a new and surprisingly useful class of low viscosity aromatic polyester polyols having an average functionality of about two, comprising the inter-esterification reaction product of at least one phthalic acid based material, at least one aliphatic diol, at least one higher functional polyol compound, and at least one hydrophobic material. The invention also relates to methods for making such aromatic polyester polyols and methods for using such aromatic polyester polyols to produce CASE materials. The invention further relates to cellular polyurethane and polyurethane/polyisocyanurate foams made using such aromatic polyester polyols. The polyester polyols of the present invention may be utilized with a wide variety of blowing agents, including water, hydrocarbon, chloroflurocarbon, and non-chlorofluorocarbon blowing agents.
The aromatic polyester polyols of the present invention can be readily blended with prior art polyols, if desired, and also with various additives conventionally used in the formulation of resin pre-polymer blends. The aromatic polyester polyols of the invention are prepared by an inter-esterification process that is simple, reliable, and well adapted for conventional chemical processing equipment.
In a first aspect, the invention provides low viscosity aromatic polyester polyols having an average functionality of about two. Thus, there is now provided an aromatic polyester polyol comprising the inter-esterification product of
(a) from about 20 to about 80 mole percent of at least one phthalic acid based material selected from the group consisting of phthalic anhydride, phthalic acid, isophthalic acid, terephthalic acid, methyl esters of phthalic, isophthalic, or terephthalic acid, dimethyl terephthalate, polyethylene terephthalate, trimellitic anhydride, pyromellitic dianhydride, maleic anhydride, or mixtures thereof;
b) from about 20 to about 80 mole percent of at least one low molecular weight aliphatic diol of the formula
HOxe2x80x94R1xe2x80x94OH
wherein R1 is a divalent radical selected from the group consisting of
i) alkylene radicals each containing from 2 through 12 carbon atoms;
ii) radicals of the formula xe2x80x94[CH2xe2x80x94R2xe2x80x94CH2]xe2x80x94 wherein R2 is a radical selected from the group consisting of 
xe2x80x83iii) radicals of the formula
xe2x80x94[(R3O)nxe2x80x94R3]
wherein R3 is an alkylene radical containing from 2-4 carbon atoms and n is an integer from 1 through 10;
or mixtures thereof;
c) from about 0.1 to about 20 mole percent of a higher functional polyol of the formula
HOxe2x80x94R4xe2x80x94OH
wherein R4 is a divalent radical selected from the group consisting of
i) radicals of the formula xe2x80x94[CH2xe2x80x94R5xe2x80x94CH2]xe2x80x94 wherein R5 is a radical selected from the group consisting of 
xe2x80x83ii) radicals selected from the group consisting of glycerine, alkoxylated glycerine, sucrose, alkoxylated sucrose, methyl glucoside, alkoxylated methyl glucoside, glucose, alkoxylated glucose, fructose, alkoxylated frutose, sorbitol, alkoxylated sorbitol, lactose, and alkoxylated lactose;
or mixtures thereof; and
d) from about 0.1 to about 20 mole percent of at least one hydrophobic material characterized by
i) having an equivalent weight of about 130-1000;
ii) containing from about 8 to 60 carbon atoms; and
iii) containing at least one and not more than four radicals per molecule, which are selected from the group consisting of carboxyl, hydroxyl, and mixtures thereof.
The inter-esterification reaction may be performed with or without a suitable esterification catalyst. Typically, and preferably, the inter-esterification reaction is performed with a suitable esterification catalyst known to those of ordinary skill in the art. Although the above components may be combined in any order to produce the low viscosity aromatic polyester polyols of the invention, in a somewhat preferred embodiment, components (a), (b), and (c) initially are combined and the inter-esterification is allowed to proceed to substantial completion, forming an intermediate polyester polyol which is then inter-esterified with component (d) to form the low viscosity aromatic polyester polyol of the present invention.
Generally, the inter-esterification reactions of the present invention are carried out under vacuum conditions, at temperatures sufficient to effect the desired esterification reaction, and water is removed from the reaction contents as the esterification proceeds. Typically, the esterification reaction is performed at a temperature of about 100xc2x0 C. to about 300xc2x0 C. More preferably, the esterification is performed at a temperature of about 180xc2x0 C. to about 220xc2x0 C.
In another aspect, the invention provides a process for producing low viscosity aromatic polyester polyols having a functionality of about two. Accordingly, there is now provided a process for producing low viscosity aromatic polyester polyols comprising inter-esterifying in any order
(a) from about 20 to about 80 mole percent of at least one phthalic acid based material selected from the group consisting of phthalic anhydride, phthalic acid, isophthalic acid, terephthalic acid, methyl esters of phthalic, isophthalic, or terephthalic acid, dimethyl terephthalate, polyethylene terephthalate, trimellitic anhydride, pyromellitic dianhydride, maleic anhydride, or mixtures thereof;
b) from about 20 to about 80 mole percent of at least one low molecular weight aliphatic diol of the formula
HOxe2x80x94R1xe2x80x94OH
wherein R1 is a divalent radical selected from the group consisting of
i) alkylene radicals each containing from 2 through 12 carbon atoms;
ii) radicals of the formula xe2x80x94[CH2xe2x80x94R2xe2x80x94CH2]xe2x80x94 wherein R2 is a radical selected from the group consisting of 
xe2x80x83iii) radicals of the formula
xe2x80x94[(R3O)nxe2x80x94R3]xe2x80x94
wherein R3 is an alkylene radical containing from 2-4 carbon atoms and n is an integer from 1 through 10;
or mixtures thereof;
c) from about 0.1 to about 20 mole percent of a higher functional polyol of the formula
HOxe2x80x94R4xe2x80x94OH
wherein R4 is a divalent radical selected from the group consisting of
i) radicals of the formula xe2x80x94[CH2xe2x80x94R5xe2x80x94CH2]xe2x80x94 wherein R5 is a radical selected from the group consisting of 
xe2x80x83ii) radicals selected from the group consisting of glycerine, alkoxylated glycerine, sucrose, alkoxylated sucrose, methyl glucoside, alkoxylated methyl glucoside, glucose, alkoxylated glucose, fructose, alkoxylated frutose, sorbitol, alkoxylated sorbitol, lactose, and alkoxylated lactose;
or mixtures thereof; and
d) from about 0.1 to about 20 mole percent of at least one hydrophobic material characterized by
i) having an equivalent weight of about 130-1000;
ii) containing from about 8 to 60 carbon atoms; and
iii) containing at least one and not more than four radicals per molecule, which are selected from the group consisting of carboxyl, hydroxyl, and mixtures thereof.
The inter-esterification reaction may be preformed with or without a suitable esterification catalyst. Typically, and preferably, the inter-esterification reaction is performed with a suitable esterification catalyst known to those of ordinary skill in the art. Although the above components may be combined in any order in accordance with the process of the present invention, in a somewhat preferred embodiment, components (a), (b), and (c) initially are combined in any order and the inter-esterification is allowed to proceed to substantial completion, forming an intermediate polyester polyol product which is then inter-esterified with component (d) to form the low viscosity aromatic polyester polyol of the present invention.
In a further aspect, the invention provides low viscosity aromatic polyester polyols having an average functionality of about two that can be mixed with polyisocyanates to yield polyurethane compositions useful as coatings, adhesives, sealants, elastomers, (CASE materials), and as potting or molding compounds.
In a still further aspect, the invention provides low viscosity aromatic polyester polyols having an average functionality of about two and having improved solubility in polyether polyols and isocyanates as compared to standard polyols such as the esterification product of phthalic anhydride and diethylene glycol alone.
As used herein, the term xe2x80x9cpolyester polyolxe2x80x9d means a polyol having ester linkages. An aromatic polyester polyol of the invention includes any minor amounts of unreacted polyol remaining after the preparation of the polyester polyol and/or any minor amounts of unesterified low molecular weight polyols (e.g., diol) added after the preparation of the polyester polyol. Although not highly preferred, the aromatic polyester polyol can include up to about 40 weight percent free diol.
The aromatic polyester polyols advantageously have an average functionality of about two. The average hydroxyl number values of the aromatic polyester polyols of the invention generally fall within a range of about 20 to about 400, preferably about 28 to about 300 and more preferably about 56 to about 225 (taking into account the free glycols that may be present). The free glycol content of the aromatic polyester polyols of the invention generally is from about 0 to about 20 weight percent, and usually from 1 to about 15 weight percent, based on the total weight of polyester polyol component.
Typically, the dynamic viscosity of the aromatic polyester polyols of the invention ranges from about 500 to about 50,000 centipoise (cps) at 25xc2x0 C. In a more preferred embodiment, the dynamic viscosity of the aromatic polyester polyols of the invention will range from about 1000 to about 10,000 cps at 25xc2x0 C.
It is possible, though less desirable, that the aromatic polyester polyols of the invention may contain small amounts of residual, non-inter-esterified phthalic acid based materials, aliphatic diols, higher functional polyols, and/or hydrophobic materials. Typically, these non-inter-esterified materials will be present in an amount of less than about 20 percent by weight, based on the total weight of the components combined to form the aromatic polyester polyols of the invention.
Phthalic Acid Based Material
The polyester polyols can be prepared using a phthalic acid based material derived (a) from substantially pure sources of the phthalic acid residues, such as phthalic anhydride, phthalic acid, isophthalic acid, terephthalic acid, methyl esters of phthalic, isophthalic, or terephthalic acid, dimethyl terephthalate, polyethylene terephthalate, trimellitic anhydride, pyromellitic dianhydride, maleic anhydride, or mixtures thereof; or (b) from more complex ingredients such as the side stream, waste or scrap residues from the manufacture of phthalic acid, terephthalic acid, dimethyl terephthalate, polyethylene terephthalate, and the like. Especially suitable compositions containing phthalic acid residues for use in the invention are (a) ester-containing byproducts from the manufacture of dimethyl terephthalate, (b) scrap polyalkylene terephthalates, (c) phthalic anhydride, (d) residues from the manufacture of phthalic acid or phthalic anhydride, (e) terephthalic acid, (f) residues from the manufacture of terephthalic acid, (g) isophthalic acid, (h) trimellitic anhydride; or combinations thereof.
The phthalic acid based material advantageously comprises at least about 30 percent by weight of phthalic acid residues. By phthalic acid residue is meant the group: 
Preferred phthalic acid based materials are selected from the group consisting of phthalic anhydride, phthalic acid, isophthalic acid, terephthalic acid, methyl esters of phthalic, isophthalic, or terephthalic acid, dimethyl terephthalate, polyethylene terephthalate, trimellitic anhydride, pyromellitic dianhydride, maleic anhydride, or mixtures thereof. Less preferably, the phthalic acid based material may be derived from a phthalic anhydride bottoms composition, a phthalic anhydride crude composition, or a phthalic anhydride light ends composition, as such compositions are defined in U.S. Pat. No. 4,529,744, the entirety of which is incorporated herein by reference.
Other useful phthalic acid based materials include, for example, polyalkylene terephthalates, especially polyethylene terephthalate (PET), or PET residues or scraps.
Still other useful phthalic acid based materials include DMT process residues, which are waste or scrap residues from the manufacture of dimethyl terephthalate (DMT). The term xe2x80x9cDMT process residuexe2x80x9d refers to the purged residue which is obtained during the manufacture of DMT in which p-xylene is converted through oxidation and esterification with methanol to the desired product in a reaction mixture along with a complex mixture of byproducts. The desired DMT and the volatile methyl p-toluate byproduct are removed from the reaction mixture by distillation leaving a residue. The DMT and methyl p-toluate are separated, the DMT is recovered and methyl p-toluate is recycled for oxidation. The residue that remains can be directly purged from the process or a portion of the residue can be recycled for oxidation and the remainder diverted from the process or, if desired, the residue can be processed further as, for example, by distillation, heat treatment and/or methanolysis to recover useful constituents which might otherwise be lost, prior to purging the residue from the system. The residue which is finally purged from the process, either with or without additional processing, is herein called DMT process residue.
These DMT process residues may contain DMT, substituted benzenes, polycarbomethoxy diphenyls, benzyl esters of the toluate family, dicarbomethoxy fluorenone, carbomethoxy benzocoumarins and carbomethoxy polyphenols. Cape Industries, Inc. sells DMT process residues under the trademark Terate(copyright) 101. DMT process residues having a different composition but still containing the aromatic esters and acids are also sold by DuPont and others. The DMT process residues to be transesterified in accordance with the present invention preferably have a functionality at least slightly greater than 2. Such suitable phthalic acid based material residues include those disclosed in U.S. Pat. Nos. 3,647,759; 4,411,949; 4,714,717; and 4,897,429; the disclosures of each of which with respect to the residues are hereby incorporated by reference.
Aliphatic Diols
The low molecular weight aliphatic diols useful in the present invention are of the formula
HOxe2x80x94R1xe2x80x94OH
wherein R1 is a divalent radical selected from the group consisting of
i) alkylene radicals each containing from 2 through 12 carbon atoms;
ii) radicals of the formula xe2x80x94[CH2xe2x80x94R2xe2x80x94CH2]xe2x80x94 wherein R2 is a radical selected from the group consisting of 
xe2x80x83iii) radicals of the formula
xe2x80x94[(R3O)nxe2x80x94R3]xe2x80x94
wherein R3 is an alkylene radical containing from 2-4 carbon atoms and n is an integer from 1 through 10;
or mixtures thereof
Examples of suitable aliphatic diols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, butylene glycols, 1,4 butanediol, 1,6-hexanediol, 1,2-cyclohexanediol, poly(oxyalkylene)polyols containing from two to four alkylene radicals derived by the condensation of ethylene oxide, propylene oxide, or any combination thereof, and the like. As those skilled in the art will appreciate, in the preparation of mixed poly(oxyethylene-oxypropylene)polyols, the ethylene and propylene oxides may be added to a starting hydroxyl-containing reactant either in admixture or sequentially. Mixtures of such diols can be employed, if desired. Preferred aliphatic diols are neopentyl glycol and diethylene glycol.
Higher Functional Polyols
The higher functional polyols useful in the present invention are of the formula
HOxe2x80x94R4xe2x80x94OH
wherein R4 is a divalent radical selected from the group consisting of
i) radicals of the formula xe2x80x94[CH2xe2x80x94R5xe2x80x94CH2]xe2x80x94 wherein R5 is a radical selected from the group consisting of 
xe2x80x83ii) radicals selected from the group consisting of glycerine, alkoxylated glycerine, sucrose, alkoxylated sucrose, methyl glucoside, alkoxylated methyl glucoside, glucose, alkoxylated glucose, fructose, alkoxylated fructose, sorbitol, alkoxylated sorbitol, lactose, and alkoxylated lactose;
or mixtures thereof.
Other examples of useful higher functional polyols include pentaerythritol and trimethylol propane.
Hydrophobic Materials
The term xe2x80x9chydrophobic materialxe2x80x9d as used herein means one or more substantially water insoluble compounds containing a substantially nonpolar organic moiety and at least one active hydrogen group, such as a hydroxyl group, a carboxylic acid group or carboxylic acid ester group.
Any hydrophobic material as above characterized can be employed, such as carboxylic acids (especially fatty acids), lower alkanol esters of carboxylic acids (especially fatty acid methyl esters), triglycerides (especially fats and oils), and the like. Mixtures of different hydrophobic materials can be employed if desired.
Preferred hydrophobic materials generally are characterized by
i) having an equivalent weight of about 130-1000;
ii) containing from about 8 to 60 carbon atoms; and
iii) containing at least one and not more than four radicals per molecule, where the radicals are selected from the group consisting of carboxyl, hydroxyl, and mixtures thereof.
Examples of fatty acids include caproic, caprylic, capric, lauric, myristic, palmitic, stearic, oleic, linoleic, linolenic, mixtures thereof, and the like. Examples of fatty acid methyl esters include methyl caproate, methyl caprylate, methyl caprate, methyl laurate, methyl myristate, methyl palmitate, methyl oleate, methyl stearate, methyl linoleate, methyl linolenate, mixtures thereof and the like.
Examples of commercially available, relatively low cost fats and oils include castor oil, coconut (including cochin) oil, corn oil, cottonseed oil, linseed oil, olive oil, palm oil, palm kernel oil, peanut oil, soybean oil, sunflower oil, tall oils, tallow, or mixtures thereof. Other suitable hydrophobic materials include dimer acid and 2-ethylhexanoic acid.
Presently preferred types of hydrophobic materials include alkyl alcohols, lower alkyl esters of fatty acids, fats, and oils. A particularly prefferred hydrophobic material is soybean oil.
Inter-esterification Catalysts
As previously indicated, the inter-esterification reaction is preferably performed using any suitable esterification catalyst known to those of ordinary skill in the art. Typically, the catalyst is present from about 0.001 to about 0.1 percent by weight, based on the total weight of all reactants. Suitable inter-esterification catalysts include, for example, acids such as sulfuric acid, phosphoric acid, para-toluene sulfonic acid; organotin compounds such dibutyl tin-(IV) dilaurate; and titanium compounds such as titanium (IV) isoproproxide. Dibutyl-tin-dilaurate and titantium (IV) isopropoxide are the preferred catalysts.
Optional Polyols
Although neither required nor necessarily preferred, polyester polyols of the present invention may be combined with other known polyols to produce polyol blends. Examples of optional polyols are thioether polyols, polyester amides and polyacetals containing hydroxyl groups, aliphatic polycarbonates containing hydroxyl groups, amine terminated polyoxyalkylene polyethers, and preferably, polyester polyols, polyester polyether polyols, polyoxyalkylene polyether polyols, and graft dispersion polyols. Mixtures of at least two of the aforesaid polyols can be used as long as the combination has an average hydroxyl number in the aforesaid range.
Optional polyoxyalkylene polyether polyols, which can be obtained by known methods, can be mixed with the polyester polyols of the present invention. For example, polyether polyols can be produced by anionic polymerization with alkali hydroxides such as sodium hydroxide or potassium hydroxide or alkali alcoholates, such as sodium methylate, sodium ethylate, or potassium ethylate or potassium isopropylate as catalysts and with the addition of at least one initiator molecule containing 2 to 8, preferably 3 to 8, reactive hydrogens or by cationic polymerization with Lewis acids such as antimony pentachloride, boron trifluoride etherate, etc., or bleaching earth as catalysts from one or more alkylene oxides with preferably 2 to 4 carbons in the alkylene radical. Any suitable alkylene oxide may be used such as 1,3-propylene oxide, 1,2- and 2,3-butylene oxide, amylene oxides, styrene oxide, and preferably ethylene oxide and 1,2-propylene oxide and mixtures of these oxides. The optional polyoxyalkylene polyether polyols may be prepared from other starting materials such as tetrahydrofuran and alkylene oxide-tetrahydrofuran mixtures; epihalohydrins such as epichlorohydrin; as well as aralkylene oxides such as styrene oxide. The optional polyalkylene polyether polyols may have either primary or secondary hydroxyl groups.
Included among the optional polyether polyols are polyoxyethylene glycol, polyoxypropylene glycol,polyoxybutylene glycol, polytetramethylene glycol, block copolymers, for example, combinations of polyoxypropylene and polyoxyethylene glycols, poly-1,2-oxybutylene and polyoxyethylene glycols, poly-1,4-tetramethylene and polyoxyethylene glycols, and copolymer glycols prepared from blends or sequential addition of two or more alkylene oxides. The optional polyalkylene polyether polyols may be prepared by any known process such as, for example, the process disclosed by Wurtz in 1859 and Encyclopedia of Chemical Technology, Vol. 7, pp. 257-262, published by Interscience Publishers, Inc. (1951) or in U.S. Pat. No. 1,922,459.
Preferred optional polyethers include the alkylene oxide addition products of polyhydric alcohols such as ethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, 1,2-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, hydroquinone, resorcinol, glycerol, 1,1,1-trimethylol-propane, 1,1,1-trimethylolethane, pentaerythritol, 1,2,6-hexanetriol, alpha-methyl glucoside, sucrose, and sorbitol. Preferred optional polyethers also include the alkylene oxide addition products of polyhydric alcohol compounds derived from phenol, such as 2,2-bis(4-hydroxyphenyl)-propane, commonly known as Bisphenol A.
All documents, e.g., patents and journal articles, cited above or below are hereby incorporated by reference in their entirety. In the following examples, all amounts are stated in percent by weight of active material unless indicated otherwise. One skilled in the art will recognize that modifications may be made in the present invention without deviating from the spirit or scope of the invention. The invention is illustrated further by the following examples which are not to be construed as limiting the invention or scope of the specific procedures or compositions described. The examples of this application disclose the reactants and their compositions along with the temperatures and reaction times which are advantageous for polyols prepared from specific components or reactants. For other reactants, these variables may be slightly different, but are easily ascertainable by those skilled in the art by routine experimentation.
The following definitions are offered for materials described herein and used in the following examples:
The acid values (AV) of the various examples are a measurement of residual acid in the final polyester polyol product. The AV values were determined by standard titration techniques. The hydroxyl value (OHV) of the various examples are a measure of the number of OH groups. The OHV values were determined by standard titration techniques. Dynamic viscosity measurement were performed using a Brookfield Viscometer. Percent water measurements were obtained by Karl-Fischer titration.